Analysis of the dynamic mutation in the SCA7 gene shows marked parental effects on CAG repeat transmission.
The gene for spinocerebellar ataxia 7 (SCA7) includes a transcribed, translated CAG tract that is expanded in SCA7 patients. We have determined expansions in 73 individuals from 17 SCA7 kindreds and compared them with repeat lengths of 180 unaffected individuals. Subjects with abnormal expansions comprise 59 clinically affected individuals and 14 at-risk currently unaffected individuals predicted to carry the mutation by haplotype analysis. For expanded alleles, CAG repeat length correlates with disease progression and severity and correlates inversely with age of onset. Increased repeat lengths are seen in generational transmission of the disease allele, consistent with the pattern of clinical anticipation seen in these kindreds. Repeat lengths in expanded alleles show somatic mosaicism in leukocyte DNA, suggesting that these alleles are unstable within individuals as well as between generations. Although dynamic repeat expansions from paternal transmissions are greater than those from maternal transmissions, maternal transmission of disease is more common, suggesting germline or embryonic effects of the repeat expansion.
Gouw
L G
LG
Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA.
Castañeda
M A
MA
McKenna
C K
CK
Digre
K B
KB
Pulst
S M
SM
Perlman
S
S
Lee
M S
MS
Gomez
C
C
Fischbeck
K
K
Gagnon
D
D
Storey
E
E
Bird
T
T
Jeri
F R
FR
Ptácek
L J
LJ
D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000483:Alleles; D000704:Analysis of Variance; D000067719:Ataxin-7; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D017931:DNA Primers; D018450:Disease Progression; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D008297:Male; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics*; D010375:Pedigree; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012016:Reference Values; D012044:Regression Analysis; D013132:Spinocerebellar Degenerations / Q000235:genetics* / Q000503:physiopathology; D014158:Transcription, Genetic; D018911:Trinucleotide Repeats
C000593829:ATXN7 protein, human; D000067719:Ataxin-7; D017931:DNA Primers; D009419:Nerve Tissue Proteins